JPH0535760B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a tanning method, and more particularly to a tanning method having two steps: pre-tanning and full tanning steps.

<Prior Art> As is currently well known, various tanning agents have been proposed and used, but chrome tanning agents and tannin tanning agents are mainly used.
Chrome tanning agents have been used since ancient times for their outstanding tanning effects, and various basic chromium sulfates based on differences in basicity and chromium content are known, and this has contributed to the development of the leather industry. has contributed greatly to.

However, even with such effective chromium tanning agents, some drawbacks have been pointed out in line with the demands of the times. The biggest problem is the environmental pollution problem caused by chromium compounds, and measures to treat chromium in tanning wastewater and leather sludge are required, and various studies are being conducted and practical applications are being promoted.

One way to combat this is to use acid-soaked rawhide with at least one type of chromium().
Chromium salt pretanning followed by pretanning in the presence of at least one acid binder using a chromium() tanning agent consisting of a formate and/or a reaction product of formic acid with chromium sulfate() Tanning methods (Special Publication No. 61-2120) have been reported.

On the other hand, the present inventor has determined that the weight ratio 0.7≦Cr ₂ O ₃ /Al ₂ O ₃
Developed a method for producing a chromium-aluminum tanning agent characterized by neutralizing an acidic mixed aqueous solution consisting of a chromium sulfate-containing substance, an aluminum salt, and a carboxylic acid compound within the range of ≦3 with an alkaline agent to make it highly basic. (Special Publication No. 60-40478).

<Problems to be solved by the invention> However, the invention of Japanese Patent Publication No. 61-2120 has a problem with the flexibility of tanned leather, and it aims to reduce the amount of chromium (Cr) in wastewater to prevent environmental pollution. There were problems such as having to do this.

On the other hand, the invention disclosed in Japanese Patent Publication No. 60-40478 improves the heat resistance of leather tanned with aluminum tanning agent alone using chromium, and also significantly reduces chromium in wastewater using the conventional chromium tanning method, reducing the chromium pollution load. However, it was found that there are some points that need to be improved as follows.

When tanning animal hides, acids are released into the solution as chromium and aluminum are adsorbed onto the hide, which tends to push the pH of the solution out of the preferred range required for a proper tanning operation, thus reducing the PH value during the tanning process. It is necessary to keep the PH of the tanning solution around a certain appropriate value by applying some kind of acid binder to the tanning solution.Adjusting the PH of the tanning solution is extremely important during tanning work, and the PH value If it is too low, the binding of chromium and aluminum to the leather will be insufficient, resulting in insufficient tanning effect.
On the other hand, if the pH value is too high, there is a danger that chromium hydroxide and aluminum hydroxide will precipitate, making it impossible to obtain high-quality tanned leather.

Therefore, in the past, an alkaline agent such as soda carbonate or bicarbonate was added to the tanning solution in several stages during the tanning process in order to adjust the pH. If the process control, such as the amount, method, and rate of addition of the alkaline agent measured at each stage, is not carefully and thoroughly controlled, the appearance and quality of the final tanned leather may be impaired, which can easily occur. It was hot.

The present inventor obtained the present invention as a result of research to solve the above problems.

<Means for Solving the Problems> That is, the present invention provides acid-soaked rawhide with chromium ()
This is a tanning method characterized by pre-tanning with salt, followed by full tanning with a chromium-aluminum tanning agent.

<Function> The present invention has two methods of performing full tanning following pre-tanning.
This is a tanning method that has two tanning steps.

The chromium () salt tanning agent used in pretanning is chromium sulfate, basic chromium sulfate, or their mirabilite-containing products, but industrially, sodium dichromate aqueous solution is used in the presence or absence of carboxylic acid. Basic chromium sulfate produced by a reduction reaction with an organic or inorganic reducing agent is suitable.

Pre-tanning involves immersing rawhide that has been subjected to the usual liming, hair removal, deashing, etc. in an aqueous solution with a pH of 2 to 4 containing an acid such as sulfuric acid and an acid swelling inhibitor such as table salt. Add chromium () salt to.

At this time, the amount of chromium () salt added must be at most 1% as Cr ₂ O ₃ based on the weight of the rawhide. This is because if the input amount is 1% or more, more than the amount of chromium deposited in the bonding reaction between skin collagen and chromium will be transferred to the wastewater, increasing the amount of chromium (Cr) in the wastewater. amount (Cr ₂ O ₃ ) 2% for 25% chrome tanning agent)
is desirable.

After adding chromium salt, drumming is performed for about 1 to 4 hours to ensure sufficient pretanning.

After the above pre-tanning yield, a full tanning is then carried out using a chromium-aluminum tanning agent.

In the present invention, chromium used in full tanning
The aluminum tanning agent contains 2 to 25% by weight of Cr ₂ O ₃ , 2 to 25% by weight of Al ₂ O ₃ , and 1 to 1 carboxylic acid compound.
Contains at least ~15% by weight, by weight
A chromium-aluminum tanning agent having a Cr ₂ O ₃ /Al ₂ O ₃ content of 0.7 to 3 and a basicity of 20 to 55%, or an acid binder of 0.2 to 100 parts by weight of the chromium-aluminum tanning agent. It is a chromium-aluminum tanning agent that has the ability to automatically adjust basicity by mixing 50 parts by weight, and the latter is usually preferred.

The above-mentioned chromium-aluminum tanning agent is made by neutralizing an acidic mixed aqueous solution consisting of a chromium sulfate-containing substance, an aluminum salt, and a carboxylic acid compound with an alkaline agent to make it highly basic, and then spray-drying it to form granules. .

Here, the chromium sulfate-containing material has the same composition as the chromium salt used in pre-tanning as described above.

Next, the aluminum salt is mainly aluminum sulfate, but other basic aluminum sulfate, aluminum chloride, basic aluminum chloride, etc. may also be used as necessary.

In addition, carboxylic acid compounds are used as masking agents for OH groups when forming a high base, for example, formic acid, acetic acid, oxalic acid,
Succinic acid, glutanic acid, adipic acid, phthalic acid,
Examples include tartaric acid, citric acid, and lactic acid, and they may also be alkali metal salts, alkaline earth metal salts, or ammonia salts, and at least one or two or more of these may be used as appropriate.

Further, the alkaline agent is not particularly limited as long as it neutralizes each of the above-mentioned chemicals to make them highly basic, but for example, caustic alkali, alkali carbonate, alkali bicarbonate, or sodium aluminate can be used. Among these, sodium bicarbonate is particularly preferred because an alkaline agent that is as mild as possible is preferable for operational purposes.

The above-mentioned chromium sulfate-containing material, aluminum salt, and carboxylic acid compound are made into a mixed aqueous solution, and then mixed and stirred with an alkaline agent at a temperature of room temperature to 80°C to gradually neutralize and make the solution highly basic.

Next, after the addition of the alkali agent is completed, the mixture is continued to be aged for a while, and if necessary, after filtering, it is spray-dried by a conventional method to form a granular product. The particle size of the product is preferably about 40 mesh which can be dissolved in cold water, but is not limited thereto.

The composition of the chromium-aluminum tanning agent obtained by the above method is preferably in the following proportions (% by weight).

Cr ₂ O ₃ 2-25% by weight (preferably 8-20% by weight) Al ₂ O ₃ 2-25% by weight (preferably 5-16% by weight) Carboxylic acid compound 1-15% by weight (preferably 6-15% by weight) Weight%) Cr203/Al203 (weight ratio) 07-3 (preferably 0.8-2) Basicity 20-55% (preferably 28-50%) The reason is that when Cr203/Al203 (weight ratio) becomes less than 0.7 As the amount of aluminum in the liquid increases, even if the masking effect of the carboxylic acid compound is relied upon during basification, aluminum hydroxide is likely to be generated during operation, making it difficult to obtain a high base level, and at the same time, production This is because the work requires extreme care, and the resulting product has an unavoidable tendency for the tanning effect to decline more than compensate for the shortcomings of chromium. This is because the benefits are not so great and they are no longer substantially different from conventional chrome tanning agents.

In addition, the content of the carboxylic acid compound used as a masking agent depends on the desired set basicity, but is also influenced by its type and the quantitative relationship between aluminum and chromium, and is less than 1%. No hardening of the masking agent was observed in the case, and 15% in the other case.
This is because even if the masking effect is exceeded, not only will no significant masking effect be observed, but it will also be disadvantageous in terms of cost.

Furthermore, the content of Cr ₂ O ₃ and Al ₂ O ₃ is Cr ₂ O ₃ /
Depends on Al ₂ O ₃ (weight ratio). In the present invention, such a chromium-aluminum tanning agent preferably has an ability to automatically adjust basicity.

This function is based on the pH level in the bath according to leather tanning.
becomes acidic, but it refers to the ability to automatically follow this PH change and maintain a predetermined PH, and this can be achieved by adding an acid binder.

As such an acid binder, calcined magnesium oxide is suitable, and natural magnesium oxide ore, calcined magnesium hydroxide or magnesium carbonate separated and collected from seawater or dolomite, calcined magnesite, magnesia clinker, etc. Examples include those whose main component is calcined magnesium oxide.

Incidentally, calcined magnesium oxide includes, for example, dolomite, alkali metal carbonate, alkali bicarbonate,
It can also be used with sodium sulfite.

These acid binders are usually used in powder form;
Reactions with free acids in tanning liquors are particularly influenced by particle size, with 100 mesh particles being preferred in most cases.
The reason for this is that particles with a particle size larger than 100 mesh remain as insoluble matter during the tanning operation, and this may deposit on the surface of the tanned leather and cause spots.

The acid binder is 0.2 parts by weight per 100 parts by weight of the chromium-aluminum tanning agent before mixing the acid binder.
It is preferable to mix up to 50 parts by weight.

The amount of the chromium-aluminum tanning agent used in full tanning may be appropriately determined depending on the flexibility of the tanned leather and the amount of chromium in the waste water and the composition of the chromium-aluminum tanning agent.

Full tanning is carried out for about 4 to 8 hours, but is not particularly limited.

The present invention will be specifically described below with reference to Examples.

<Examples> Example 1 Bovine hide (100 parts by weight) that had been limed, depilated, and demineralized in a conventional manner was acidified using common salt, sulfuric acid, and 60 parts of water. The pH at this time was 2.6. To this, 2 parts of chromium salt (Neochrome, manufactured by Nihon Kagaku Kogyo Co., Ltd.) Cr ₂ O ₃ 25%, basicity 33.3%) was added,
Time drummed. Next, 5 parts of the chromium-aluminum tanning agent shown below was added and drumming was carried out for 6 hours. Two hours after the addition of the chromium-aluminum tanning agent, sodium bicarbonate was added in four portions every 30 minutes to bring the final pH to 4.1. The temperature at this time is
It was 38℃. The resulting tanned leather contains _1.96 % _Cr2O3 ,
The Al ₂ O _{3 content} was 1.24%, the heat shrinkage temperature was 112°C, and the chromium (Cr) in the tanning wastewater was 102 ppm. Finishing in a conventional manner resulted in a flexible, soft-feeling leather.

<Preparation of chromium-aluminum tanning agent> In a glass-lined reactor equipped with a thermometer and a stirrer Water 4655Kg Basic chromium sulfate (Neochrome manufactured by Nihon Kagaku Kogyo) 1000Kg Aluminum sulfate (Al ₂ (SO ₄ ) ₃ 57%) 2138Kg of sodium formate (HCOONa95%) 376Kg were taken, heated to 60°C, and stirred and mixed for 60 minutes. To this mixture, 599 kg of bicarbonate of soda was gradually added over 180 minutes to make it highly basic. After addition, the mixture was filtered according to a conventional method and then spray-dried to obtain 3172 kg of dried granules. The composition of this dried granular material was as follows.

Cr ₂ O ₃ 8.0% by weight Al ₂ O ₃ 11.4% by weight HCOONa 11.2% by weight Cr203/Al203 (weight ratio) 0.7 Basicity 33.3% Example 2 Bovine hide (100 parts by weight ) was pickled using common salt, sulfuric acid and 60 parts of water. The pH at this time was 2.6. To this, 2 parts of chromium salt (Neochrome, manufactured by Nihon Kagaku Kogyo Co., Ltd.) Cr ₂ O ₃ 25%, basicity 33.3%) was added,
Time drummed. Next, 5 parts of the chromium-aluminum tanning agent shown below was added and drumming was carried out for 6 hours. Two hours after the addition of the chromium-aluminum tanning agent, sodium bicarbonate was added in four portions every 30 minutes to bring the final pH to 4.1. The temperature at this time is
It was 38℃. The resulting tanned leather _contains 1.42% _Cr2O3 ,
The Al ₂ O ₃ content was 1.06%, the heat shrinkage temperature was 108°C, and the chromium (Cr) in the tanning wastewater was 93 ppm. Finishing in a conventional manner resulted in a flexible, soft-feeling leather.

<Preparation of chromium-aluminum tanning agent> In a glass-lined reactor equipped with a thermometer and a stirrer Water 2461Kg Basic chromium sulfate (manufactured by Nihon Kagaku Kogyo Co., Ltd. Neochrome) 1000Kg Aluminum sulfate (Al ₂ (SO ₄ ) ₃ 952Kg of sodium formate (HCOONa95%) and 254Kg of sodium formate (HCOONa95%) were taken, heated to 60°C, and stirred and mixed for 60 minutes. To this mixed solution, 267 kg of bicarbonate of soda was gradually added over 180 minutes to make it highly basic. After addition, the mixture was filtered according to a conventional method and then spray-dried to obtain 2014 kg of dried granules. The composition of this dried granular material was as follows.

Cr ₂ O ₃ 12.6% by weight Al ₂ O ₃ 8.0% by weight HCOONa 11.9% by weight Cr203/Al203 (weight ratio) 1.58 Basicity 33.3% 1217Kg of calcined magnesium oxide (MgO95.0%) was added to 2014Kg of this granular dry material, and the mixture was homogenized. until
By mixing, 2135 kg of chromium-aluminum tanning agent was obtained.

The composition of this chromium-aluminum tanning agent was as follows.

Cr ₂ O ₃ 11.9% by weight Al ₂ O ₃ 7.5% by weight HCOONa 11.2% by weight MgO 5.4% by weight Basicity 61.8% <Effects of the Invention> According to the method of the present invention, the tanning agent can penetrate well into the inside of the tanned leather. The distribution of chromium and aluminum becomes uniform, and a well-finished leather with a flexible silver surface and good tightness is obtained.

Furthermore, the amount of chromium used can be reduced, and the amount of chromium in wastewater can be reduced to at least one-fifth of the conventional method, significantly improving the amount of chromium contamination, making it easier to take environmental measures for wastewater.

Claims (1)

[Scope of Claims] 1. A tanning method characterized by pre-tanning pickled rawhide with chromium () salt and then performing full tanning with a chromium-aluminum tanning agent. 2. The tanning method according to claim 1, wherein the chromium-aluminum tanning agent has an automatic basicity adjustment ability.